1. The Field of the Invention
The present invention relates to a construction of a rotating electric machine. Particularly, the present invention relates to an improvement of a high-resolution and high-accuracy hybrid stepping motor of an outer rotor type or an inner rotor type that is suitable for OA equipment, which requires accurate positioning during high speed operation, such as a printer, a high speed facsimile or a PPC copying machine.
2. Prior Art
The hybrid stepping motor that is a combination of a permanent magnet stepping motor and a variable reluctance stepping motor provides high accuracy, large torque and little step angle. For example, a conventional hybrid stepping motor of an inner rotor type (a motor for short in the following description) has the construction as shown in FIGS. 35 and 36.
FIG. 35 is a longitudinal sectional front view of one example of this kind of conventional motor, and FIG. 36 is a sectional view of FIG. 35 along XXXVIxe2x80x94XXXVI line.
In FIGS. 35 and 36, a symbol 21 represents a cylindrical casing and the casing 21 is integrally fixed to a stator iron-core 22 formed of magnetic material. A predetermined number of magnetic poles 23 corresponding to construction characteristic of this motor are centripetally formed around the inner circumference of the stator iron core 22 at equal pitches. A winding 24 to magnetize the magnetic pole 23 is wound around each of the magnetic poles 23.
Further, pole teeth 23a whose number corresponds to the construction characteristic of this motor are formed on a tip of each magnetic pole 23 at equal pitches.
In general, the stator iron-core 22 and the magnetic pole 23 are manufactured by punching a magnetic material plate with a punch press. A predetermined number of the punched plates are stacked and the winding 24 is wound to shape a stator.
End plates 25 and 26 are integrally connected to both ends of the casing 21.
A pair of bearings 27a and 27b are mounted on the center of the end plates 25 and 26, which rotatably support a rotor axis 28.
A permanent magnet 29 that is magnetized in the axial direction is engaged and fixed to the rotor axis 28. The permanent magnet 29 is sandwiched between two rotor magnetic poles 30A and 30B having disc shapes. Around an outer circumference of each of the rotator magnetic poles 30A and 30B, pole teeth 30a are formed such that the shapes and the intervals thereof correspond to that of the pole teeth 23a formed on the magnetic pole 23 of the stator. The first and second rotor magnetic poles 30A and 30B are engaged such that the pole teeth 30a of the first rotor magnetic pole 30A and the pole teeth 30a of the second rotor magnetic pole 30B are deviated by xc2xd pitch.
In general, the magnetic pole of the rotor is manufactured by punching a magnetic material plate with a punch press. A predetermined number of the punched plates are stacked to shape a rotor.
In the motor having the above described configuration, when the windings 24 of the stator are sequentially energized in the predetermined order, each of the pole teeth 23a of the stator are magnetized in sequence. Accordingly, the rotor rotates and stops as the magnetic field caused by the magnetized pole teeth 23a of the stator varies according to the interaction between the respective pole teeth 23a of the stator and the respective pole teeth 30a of the rotor that are magnetized by the permanent magnet 29.
Number of the magnetic poles 23 of the stator, number of the pole tooth 23a and number of the pole teeth 30a of the rotor vary depending on conditions such as number of phase of the motor.
FIG. 37 shows a connection example of a conventional 6-phase motor with monofier (unifier) windings and twelve lead lines drawn therefrom.
The numbers applied to the upper portion of the drawing represent the magnetic pole windings, assuming that the predetermined magnetic pole winding is referred to as 1E and the next one is referred to as the next number in order until the number reaches 24E.
The connection for each magnetic pole winding is shown in FIG. 37. The magnetic pole windings 1E, 7E, 13E and 19E are connected in series between the lead lines A and Axe2x80x2 such that the magnetic pole windings 1E, 13E are in opposite phase to the magnetic pole windings 7E, 19E. The magnetic pole windings 2E, 8E, 14E and 20E are connected in series between the lead lines B and Bxe2x80x2 such that the magnetic pole windings 2E, 14E are in opposite phase to the magnetic pole windings 8E, 20E. The magnetic pole windings 3E, 9E, 15E and 21E are connected in series between the lead lines C and Cxe2x80x2 such that the magnetic pole windings 3E, 15E are in opposite phase to the magnetic pole windings 9E, 21E. The magnetic pole windings 4E, 10E, 16E and 22E are connected in series between the lead lines D and Dxe2x80x2 such that the magnetic pole windings 4E, 16E are in opposite phase to the magnetic pole windings 10E, 22E. The magnetic pole windings 5E, 11E, 17E and 23E are connected in series between the lead lines E and Exe2x80x2 such that the magnetic pole windings 5E, 17E are in opposite phase to the magnetic pole windings 11E, 23E. The magnetic pole windings 6E, 12E, 18E and 24E are connected in series between the lead lines F and Fxe2x80x2 such that the magnetic pole windings 6E, 18E are in opposite phase to the magnetic pole windings 12E, 24E.
An excitation electric current is sequentially applied to the respective lead lines.
FIG. 38 shows an example of an excitation sequence of one-phase excitation for the connection shown in FIG. 37.
In FIG. 38, the symbols of the lead lines shown in FIG. 37 to which an exciting current is applied are shown in the vertical direction and the excitation steps are shown at the upper portion in the horizontal direction. The rectangles above the respective lines in the horizontal direction represent that an electric current passes through the lead lines in the predetermined direction, and the rectangles below the respective lines represent that an electric current passes through the lead lines in the opposite direction.
In the drawing, an electric current passes from the lead line A shown in FIG. 37 to the lead line Axe2x80x2 at step 1, and, at the next step 2, an electric current passes from the lead line B to the lead line Bxe2x80x2. After that, an electric current flows step by step until step 6, and an electric current passes in a direction from the lead line Axe2x80x2 to the lead line A at step 7. Then, an electric current is applied to each lead line in the same manner to excite each magnetic pole of the stator in turn.
Accordingly, since magnetic polarity of each magnetic pole of the stator varies, the magnetic pole of the stator attracts the corresponding magnetic pole (pole teeth) of the rotor, which rotates the rotor axis 28 of the motor.
Further, FIG. 39 shows an example of a connection of windings in a conventional 10-phase motor with a monofier (unifier) winding, and FIG. 40 shows an example of an excitation sequence of one-phase excitation for the 10-phase motor with monofier winding shown in FIG. 39. How to read is the same as FIGS. 37 and 38 that are described above.
A step angle xcex8s, which is a basic characteristic of the above described stepping motor, is determined by the following equation (1).
xcex8s=180xc2x0/(Mxc3x97Z)xe2x80x83xe2x80x83(1) 
Where M is phase number of the stator and Z is number of pole teeth of the rotor.
The above described inner rotor motor is constructed such that the rotor is located at the center of the motor and the stator is arranged around thereof. On the other hand, an outer rotor motor is constructed such that the stator is located at the center of the motor and the rotor is arranged around thereof. As a result, the structure of the rotating mechanism of the outer rotor motor is different from that of the inner rotor motor, while the basic construction to generate a torque of the outer rotor motor is similar to that of the inner rotor motor.
FIG. 41 is a vertical sectional view of the outer rotor motor and FIG. 42 is a sectional view along XXXXIIxe2x80x94XXXXII line of FIG. 41. FIGS. 41 and 42 correspond to FIGS. 35 and 36 that show the inner rotor motor, respectively. In FIGS. 41 and 42, a symbol 101 represents a cylindrical stator support that is supported by a fixing member (not shown). A symbol 102 represents a stator iron-core that is fixed to the stator support 101, and a plurality of stator magnetic poles 102a are arranged around the stator iron-core 102. Pole teeth 102b are formed on a circumference of this stator magnetic pole 102a. A symbol 103 represents a winding that is wound around each magnetic pole 102a. 
In FIG. 42, the windings 103 are illustrated in schematic forms and a symbol xe2x80x9cxxe2x80x9d located in the winding means that an electric current passes from the front side of the sheet to the back side and a symbol xe2x80x9cxc2x7xe2x80x9d means that an electric current passes from the back side to the front side.
A symbol 104 represents a rotor casing that consists of an annular portion 104a and a side plane portion 104b. A symbol 105 represents a rotor axis whose one end is fixed to the center of inner side of the side plane portion 104b of the rotor casing 104, and it is rotatably supported by the inner circumference of the stator support 101 through a bearing 106. A symbol 107 represents a permanent magnet, and rotor magnetic pole 108a, 108b are connected to the both side surfaces thereof. On the internal circumferences of the rotor magnetic poles 108a and 108b, pole teeth 108c and 108d, which are deviated in xc2xd pitch of phase, are formed at the positions facing pole teeth 102b of the stator magnetic pole 102a. 
In the following description, the respective embodiments are explained as inner rotor motors and outer rotor motors will not be described because they can be accomplished according to the description of the inner rotor motors.
The U.S. Pat. No. 3,206,623 discloses an electric synchronous inductor motor.
The electric synchronous inductor motor disclosed in the patent includes a pair of stators having identical construction and a pair of rotors having identical construction. Each stator is the circular electrode structure that is provided with magnetic poles that are centripetally formed in an inward direction. Each magnetic pole has pole teeth formed at equal pitches on the tip end thereof. The magnetic poles are wound by windings. Each rotor consists of a permanent magnet that is magnetized in the axial direction and a pair of end caps (magnetic pole plates) arranged at both sides of the permanent magnet. The end cap is provided with pole teeth around the outer circumference. The permanent magnet and the end caps are connected to a rotor axis. Magnetic coupling between the rotors is shielded. The pole teeth of one end cap are deviated from the pole teeth of the other end cap by xc2xd pitch of the pole teeth.
The above described step angle xcex8s is a rotation angle when the windings of one phase are excited by applying power in sequence, and it is determined by the motor construction.
Accordingly, it is necessary to minimize the step angle to obtain a motor having high resolution and a good control performance.
Incidentally, since the step angle xcex8s of the conventional motor (hybrid stepping motor) is represented by the above equation (1), the phase number M or the number of pole teeth Z of the rotor must be larger to minimize the step angle xcex8s. For example, when the number of pole teeth equals 50, the step angle of the 2-phase motor (hybrid stepping motor) becomes
xcex8s=180xc2x0/2xc3x9750=1.8xc2x0, 
the step angle of the 3-phase motor becomes
xcex8s=180xc2x0/3xc3x9750=1.2xc2x0, and 
the step angle of the 5-phase motor becomes
xcex8s=180xc2x0/5xc3x9750=0.72xc2x0. 
Incidentally, since a rotor is formed by a punch press in general as described above, the number of pole teeth of the rotor is determined by a manufacturing technology such as an accuracy of the punch press. Accordingly, since the number of pole teeth is limited by the manufacturing technology, the upper limit is about 100.
Further, when the phase number increases, a 6-phase motor requires 24 stator magnetic poles and a 10-phase motor requires 40 stator magnetic poles. Since the slot area becomes smaller as the number of magnetic pole becomes larger, there is a problem that a cross-section area of a winding, i.e., quantity of cooper becomes small to obtain a small motor. Further, there is a problem that a manufacturing cost becomes higher because a complicated work is required in a winding process and the number of man-hours increases.
Accordingly, a 5-phase motor was a upper limit on practical use of a small hybrid stepping motor. The step angle xcex8s (resolution) of a 5-phase motor becomes
xcex8s=180xc2x0/5xc3x97100=0.36xc2x0, 
according to the equation (1) when the number of pole teeth equals 100.
A micro-step driving is needed to get a resolution smaller than 0.36 degrees. However, since the stop position of the rotor is determined by the relative values of electric current applied to the respective phases under the micro-step driving, it was difficult to improve the accuracy of the resolution due to variation of the values of electric current applied to the respective phases, variation of characteristics of switching elements, or the like. Further, since a complicated drive circuit was need for the micro-step driving, there was a problem that the cost rises.
Further, the electric synchronous inductor motor disclosed in the U.S. Pat. No. 3,206,623 consists of two motor constructions connected in the axial direction each of which includes a stator and a rotor whose constructions are similar to the conventional stepping motor as shown in FIGS. 35 and 36 in order to obtain double the torque of the conventional electric synchronous inductor motor. The motor employing this technique can be driven by pulse power as well as a stepping motor, while it cannot rotate accurately because of the low resolution.
In the above description, while the problems of the inner rotor stepping motor are described, there are the same problems for an outer rotor stepping motor.
Furthermore, there was not the appropriate operational expression that decides the number of pole teeth of a rotor for the conventional hybrid stepping motor of inner rotor type or outer rotor type. As a result, since not all motors have desired performance, the manufacturing yield was inadequate.
An object of the present invention is to solve the above described problems of the conventional motor. That is, the object of the present invention is to increase a phase number without increasing a number of magnetic poles and thereby to provide a high-resolution and high-accuracy motor (a stepping motor) without increasing the size of the motor and without forming a complicated driving circuit on condition that a number of pole teeth of a rotor is determined by a specific relationship with numbers of the phase and the magnetic poles of a stator.
An inner rotor hybrid stepping motor of 6-phase/6 m-pole type according to the present invention described in claim 1 comprises: a stator comprising an annular magnetic substance, 6 m pieces of stator magnetic poles that are centripetally formed around the inner circumferential surface of said annular magnetic substance toward the center at equal pitches and each stator magnetic pole having a plurality of pole teeth formed on the inner tip end thereof at equal pitches, and excitation windings being wound around said stator magnetic poles; a rotor, which is rotatably supported by said stator through a predetermined air gap with respect to the inner circumferential surface of said stator pole teeth, having a cylindrical permanent magnet magnetized in an axial direction that is sandwiched between a pair of rotor magnetic poles each having rotor pole teeth corresponding to said stator pole teeth;
wherein said stator magnetic poles include first magnetic poles whose pole teeth formed on the inner tip ends are line-symmetric with respect to the shape of said magnetic poles and second magnetic poles whose pole teeth are formed on the inner tip ends at the same pitches and the same number as said pole teeth of said first magnetic poles and said pole teeth of the second magnetic poles are deviated from the pole teeth of said first magnetic poles by xc2xc pitch in the same circumferential direction, said first and second magnetic poles are alternatively arranged in the circumferential direction, and said stator containing said first and second magnetic poles is divided into a first stator portion and a second stator portion that are arranged in the axial direction, and said first and second magnetic poles of said first stator portion are connected to said second and first magnetic poles of said second stator portion, respectively, in the axial direction, while said first and second stator portions are inverted in the front and back in the circumferential direction;
wherein said rotor includes first and second rotor units that face the inner circumferential surfaces of pole teeth of said first and second stator portions with said air gap, each of said first and second rotor units is provided with a permanent magnet magnetized in the axial direction that is sandwiched between coaxial first and second rotor magnetic poles, said first and second rotor magnetic poles have rotor pole teeth around the outer circumferential surface thereof, the number of said rotor pole teeth corresponds to that of said stator pole teeth, said first rotor magnetic pole is deviated from said second rotor magnetic pole by xc2xd of the rotor teeth pitch, and said first and second rotor units are connected in the axial direction through a non-magnetic material member such that they are deviated from each other by xc2xc of the rotor teeth pitch;
and wherein the number of said rotor pole teeth Z satisfies the following condition (2);
Z=m(6n+1) or Z=m(6n+2)xe2x80x83xe2x80x83(2) 
where m and n are integers equal to or larger than 1.
Further, in the invention described in claim 2, 6-phase/6 m-pole type of claim 1 is replaced with 10-phase/10 m-pole type and the following condition (3) is satisfied;
Z=m(10n+2) or Z=m(10n+3)xe2x80x83xe2x80x83(3) 
where m and n are integers equal to or larger than 1.
Further, the outer rotor hybrid stepping motors of claims 3 and 4 are constructed that the rotors of the inner rotor hybrid stepping motors of claims 1 and 2 are arranged outside the cylindrical stators, respectively.
Further, the inner rotor or outer rotor hybrid stepping motor of claim 5 is characterized in that each stator comprises a predetermined number of stacked magnetic material plates each of which has h/2 pieces of magnetic poles whose pole teeth formed on the tip ends are line-symmetric with respect to the shape of said magnetic poles of a predetermined size and h/2 pieces of magnetic poles whose pole teeth are deviated by xc2xc of the pole teeth pitch in the same circumferential direction that are alternatively arranged; a predetermined number of stacked magnetic material plates having the same constructions as said magnetic material plates that are rotated by 180/h degrees, said stacked elements are fixed to each other; and windings that are wound around said magnetic poles. Where h equals 6 m or 10 m and m is an integer equals to or larger than 1.
Further, the inner rotor or outer rotor hybrid stepping motor of claim 6 is characterized in that said stator pole teeth pitch xcfx84S and said rotor pole teeth pitch xcfx84R satisfy the following condition (4):
0.75 xcfx84Rxe2x89xa6xcfx84Sxe2x89xa61.25 xcfx84Rxe2x80x83xe2x80x83(4) 